Diversifying crop rotations with temporary grasslands - Université de ...

On average, the 3-year rotations had highest total weed seed densities and species diversities,
probably due to the strongly reduced herbicide inputs and diversified crop sowing dates in this
system, while the plant communities in continuous corn had lowest species diversity and
evenness (high abundances prevalence of single weed species such as C. album) and grasses
were more frequent in the rotations including hay crops. Moreover, several interactions
between the rotation and tillage treatments were significant.
Bellinder et al. (2004) compared the weed seed banks before and after four 2-year crop
rotations including alfalfa, clover (Trifolium pratense L.), rye (Secale cereale L.), and sweet
corn (Zea mays L. var. rugosa Bonaf.) with a rye cover crop at three sites in New York, USA.
Weed seed banks increased in all four systems. Increases were highest in rye, while seed bank
densities did not differ between the two mown forage crops and corn, although pre- and post
emergence herbicides and soil tillage (disking) was used only in corn.
Teasdale et al. (2004) and Cavigelli et al. (2008) compared the weed seed banks during 6
years between three crop rotations: (i) a 2-year corn (Zea mays L.)–soybean [Glycine max (L.)
Merr.] rotation, (ii) a 3-year corn–soybean–wheat (Triticum aestivum L.) rotation, and (iii) a
4+-year corn–soybean–wheat–red clover + cocksfoot (Trifolium pratense L. + Dactylis
glomerata L.) hay rotation. Annual dicotyledonous species including Amaranthus hybridus L.
and C. album, the most harmful weeds in these systems, showed reduced seed bank densities
after the hay phase while some annual grasses showed the opposite effect. The weed
suppressive effects were strongest when the 4-year rotations started with hay crops.
Stevenson et al. (1997; , 1998) found greater weed species diversity in a barley/forage rotation
compared to a barley monoculture. The barley-forage rotation showed increase in barley dry
weight seed yield (+ 29% and + 26% compared to the monoculture) in all years except one,
despite greater weed pressure in the barley-forage rotation, suggesting benefits of forages to
subsequent annual crops.
Albrecht (2005) analyzed the weed seed banks during 8 years on a farm recently converted to
organic practices in Bavaria, Germany. On average, rotated grass-clover forage crops
(undersown in winter cereals, lasting 1.5 years) reduced the seed bank density by 39%, winter
cereals (wheat or rye, Secale cereale L.), sunflowers ( Helianthus annuus L.) and lupins
(Lupinus albus L.) increased it by 30-40% per year and potatoes (Solanum tuberosum L.) and
sown fallows caused no significant changes.
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